Extraction of gallium using a trialkyl pohosphate



United States Patent 6 Claims. 61. 23-312 This invention relates to a process for the recovery of gallium. More particularly, this invention relates to a process of treating a solution containing a small amount of gallium together with a relatively large amount of iron to increase the gallium content of the said solution.

Gallium is generally present in a small amount in aluminum-containing ores, and in order for smelting the gallium, it must be separated from a large amount of aluminum. For this purpose a variety of methods have been proposed heretofore. Any of these methods permit the separation of gallium from aluminum, but a problem still to be resolved is the separation of gallium from iron. Gallium is also present in zinc ores, coal and the like. In cases when gallium is recovered from these raw materials, it is required to separate the gallium from a large amount of aluminum or iron.

In order to separate gallium from a large amount of iron, the following method has been employed heretofore on an industrial scale. This method is based on the property that While gallium as Well as aluminum dissolves in caustic soda, iron becomes ferrite hydroxide and does not dissolve. Accordingly this known method necessitates the use of a large amount of caustic soda. Furthermore, if a large amount of iron exists, a part of the gallium will coprecipitate with the iron which is a disadvantage. In addition to this, if aluminum is present, the known method which provides for separation of gallium from iron must be followed by an additional process in which separation of gallium from aluminum is effected. Thusjboth aluminum and gallium dissolved in caustic soda are neutralized with an acid and then the resulting precipitate is treated with concentrated hydrochloric acid and then extracted with a solvent. Such process disadvantageously requires duplicated procedures and use of expensive reagents.

In order to overcome the drawbacks in the prior art, applicants have found a new process for recovering or separating gallium from a solution containing gallium together with aluminum and/ or iron.

In accordance with a process of the present invention, gallium which coexists together with iron or iron and aluminum is treated with hydrochloric acid and the resulting solution is extracted with a solvent, i.e., trialkyl phosphate or the dilute solution thereof, in an amount of less than that which is consistent with the amount of the iron, whereby the gallium is separated from the aluminum and the major part of said iron.

Trivalent iron and gallium in the hydrochloric acid solution can be extracted with trialkyl phosphate or the dilute solution thereof, whereas aluminum can not be extracted independent upon the concentration of the said hydrochloric acid solution. In case where iron and gallium are extracted from the hydrochloric acid solution with the above-indicated solvent, the partition ratio between iron and gallium, of course, will vary depending on the concentration of the hydrochloric acid solution. In one example, gallium is barely extracted with a 20% tributyl phosphate-kerosene solution at the hydrochloric acid concentration of less than 3 N. For the extraction of iron with the same solvent, a hydrochloric acid concentration of more than 2 N, is preferred. Below this 3,151,946 Patented Oct. 6, 1964 ice lower limit, eflicient extraction of iron is diflicult. If the iron or gallium content is relatively low, the increased hydrochloric acid concentration of the solution generally improves the partition ratio and the equilibrium inclines to the side of the solvent phase.

When iron is extracted with trialkyl phosphate, this solvent has a limited extraction capacity. In other words, if the solvent is saturated with iron, it can not extract any further iron. Accordingly, insofar as the iron concentration is low and the solvent is not yet saturated, the partition ratio will be improved in response to the increase in the hydrochloric acid concentration. But, if the iron concentration is high and the solvent becomes saturated with iron, no change is found in the solvent phase at a hydrochloric acid concentration as high as 3 to 4 N or higher by increasing the ferric chloride or hydrochloric acid concentration. At this stage, even if the iron concentration at the side of the hydrochloric acid solution is increased beyond an extent capable of saturating the solvent, the additional portion of iron remains at the hydrochloric acid side and it does not transfer to the solvent side.

When an excess of iron is present in the hydrochloric acid phase and the solvent is saturated with iron, the addition of a small amount of gallium to this system makes partition of gallium to both of the hydrochloric acid and the solvent by the replacement of a part of the iron With the added gallium in spite of the saturation of the solvent with iron. The partition ratio thereby obtained may be changed in a considerably Wide range depending on the concentration of the hydrochloric acid. But, if the hydrochloric acid concentration is selected at a proper value, the major part of gallium can be transferred to the solvent side although a large amount of iron remains at hydrochloric acid side. In this case, the partition ratio of gallium may be affected by the iron concentration in the hydrochloric. acid as well as the hydrochloric acid concentration. Generally if the iron concentration becomes higher, the partition of gallium into the solvent decreases.

Not only is the partition ratio of gallium into the solvent decreased by an increase of the iron concentration in hydrochloric acid phase, but also the optimum range of hydrochloric acid concentration for partition of gallium is lowered. If the hydrochloric acid concentration is out of the optimum range, the partition ratio of gallium is extremely decreased. For example, the optimum range of hydrochloric acid concentration for extraction of a trace amount of gallium dissolved in a hydrochloric acid solution containing 17.8 mg. Fe+++/ ml. in the form of ferric chloride with one-fourth volume, based on that of the aqueous phase, of 20% TBP-kerosene solution, is from 4.5 to 7 N. Out of this optimum range, the partition ratio of gallium rapidly decreases. In the similar system as above, the iron concentration is increased to 32.1 mg. Fe+++ (FeCl )/ml. of this solution and correspondingly the optimum hydrochloric acid concentration is 46 N. When 32.1 mg. Fe+++/ml. is employed, the maximum partition ratio of gallium may be about 40% of that which is obtained by employing 17.8 mg. Fe+++/ml. as an iron concentration. In response to further increase of the iron concentration, the partition ratio of gallium decreases.

The coexistance of aluminum in the hydrochloric acid has little influence on the partition ratio of gallium, but the increase of the aluminum concentration also lowers the optimum range of the hydrochloric acid concentration. All these properties as stated above are the basis of the present invention. Hydrochloric acid solution, in which a large quantity of iron with or without aluminum is dissolved, is adjusted at the proper hydrochloric acid concentration and then subjected to solvent extraction with trialkyl phosphate or the dilute solution thereof in such amount that it is saturated with a part of iron present. The major part of iron with or without the Whole part of aluminum remains in the hydrochloric acid phase, while the minor part of iron and the major part of gallium are extracted into the solvent phase. When the thus treated solvent is washed with water, the iron and gallium in the solvent will readily dissolve in the aqueous phase. By repeating these procedures or by carrying out countercurrent multi-stage extraction, the amount of gallium remaining in the hydrochloric acid or the amount of iron accompanying to the gallium can be decreased. Thus, gallium can be separated from a substantial part of the iron or from iron and aluminum in the hydrochloric acid. The use of the solvent in an amount as small as possible is effective to decrease the amount of iron accompanying the extracted gallium, and this is desirable for separating of gallium from the accompanying iron subsequent to an initial separation of the gallium from a substantial part of iron. v

If the hydrochloric acid concentration is high, trialkyl phosphate simultaneously extracts hydrochloric acid too. In the multi-stage extraction, therefore, this simultaneous extraction effect must be taken in consideration to keep the hydrochloric acid concentration within the optimum range. For this purpose, it is suitable to have a stoichiometrically sufiicient amount of hydrochloric acid dissolved in the solvent to provide equilibrium within the system by the pretreatment of said solvent with hydrochloric acid.

For additional information, the optimum range of a free hydrochloric acid concentration may vary depending on the concentration of coexisting chlorides, but it generally is less than N and usually Within the range of from 2 to 9 N. A desirable ratio of iron and gallium in the hydrochloric acid solution to be treated is more than about 10 times and particularly more than thirty times. Although the coexistence of aluminum will affect the optimum range of hydrochloric acid concentration, the present invention is applicable for all ranges of aluminum concentration.

Example I 200 ml. 6 N hydrochloric acid solution containing chlorides equivalent to 17.8 mg. Fe+++/ml. and 0.072 mg. Ga/ml. (Ga/Fe O =0.234%) were placed in a separating funnel and then subjected to solvent extraction using 50 ml. of 20% TBP-kerosene solution. The aqueous phase was removed, and the solvent phase was washed with 25 ml. of water to effect back-extraction of iron and gallium into washing water. The collected washing water contained 31.9 mg. Fe+++/ml. and 0.495 mg. Ga/ml. (Ga/Fe O =l.09%). After the solvent extraction, the residual hydrochloric acid solution contained 13.8 mg. Fe+++/ml. and 0.010 mg. Ga/ml. (Ga/Fe o =0.051%).

Example 2 200 ml. of 5.7 N hydrochloric acid solution containing chlorides equivalent to 17.8 mg. Fe+++/ml., 0.033 mg. Ga/ml. and 58.0 mg. Al/ ml. were placed in a separating funnel and then subjected to solvent extraction using 50 ml. of 20% TBP-ligroin solution. The aqueous phase was removed, and the solvent phase was washed with water to have back-extraction of gallium and iron into washing water. The collected washing water contained 15.9 mg. Fe+++/ml. and 0.102 mg. Ga/ml. After the solvent extraction the residual hydrochloric acid solution contained 13.8 mg. Fe+++/ml., 58.0 mg. Al/ml. and 0.007 mg. Ga/ml.

Example 3 50 ml. of 5.7 N hydrochloric acid solution containing chlorides equivalent to 32.1 mg. Fe+++/ml. and 0.026 mg. Ga/rnl. were placed in a separating funnel and then subjected to solvent extraction using 5 ml. of TBP. The aqueous phase was removed, and the solvent phase was back-extracted four times with 5 ml. of water. The aqueous back-extracts were combined and then washed with ligroin to remove a little amount of TBP contained therein. The aqueous extract obtained was 21 ml. and contained 16.6 mg. Fe+++/ml. and 0.053 mg. Ga/ml. After the TBP extraction, the residual hydrochloric acidsolution was washed with ligroin. 49 ml. of clear solution was obtained, which contained 25.6 mg. Fe+++/ml. and 0.0035 mg. Ga/ml.

Example 4 5.7 N hydrochloric acid solution containing chlorides equivalent to 31.2 mg. Fe +++/ml. and 0.026 mg. Ga/ml. was subjected to counter-current three-stage extraction using, at the aqueous-to-organic liquid ratio of 6.7, 20% TBP-kerosene solution. The solvent phase into which gallium and iron were extracted was then back-extracted with /2 times amount of water, whereby the gallium and iron were taken up in aqueous phase. The iron and gallium concentrations in the aqueous phase were 30.0 mg. Fe+++/ml. and 0.302 mg. Ga/ml. respectively. The residual hydrochloric acid solution contained 29.8 mg. Fet /ml. and 0.003 mg. Ga/ml. after the extraction.

What we claim is:

1. A process for separating and extracting gallium from a major portion of ferric chloride coexisting therewith in an aqueous hydrochloric acid solution which comprises adding trialkyl phosphate solvent having 8 to 25 carbon atoms to a hydrochloric acid solution containing gallium chloride together with ferric chloride, the latter in an amount between 10 and 1000 times the equivalent of the gallium, and where the concentration of said hydrochloric acid solution is such that the total chlorine ion concentration is between 5.0 N to 10.0 N the amount of free hydrochloric acid the concentration of free hydrochloric acid is less than .7.0 N, but greater than the molar amount of gallium included and the molar amount of said trialkyl phosphate is 0.15 to 1.5 times the molar amount of ferric chloride in the aqueous phase, said trialkyl phosphate solvent being effective to extract a major portion of gallium in the aqueous phase together with a minor portion of ferric chloride, washing with water the solvent after the extraction, whereby the gallium and ferric chloride are extracted from the solvent and the solvent may be used for the extraction of gallium and ferric chloride from a fresh hydrochloric solution.

2. A process for separating and extracting gallium from a major portion of ferric chloride coexisting therewith in a hydrochloric acid solution which comprises adding trialkyl phosphate solvent having 8 to 25 carbon atoms to a hydrochloric acid solution containing gallium chloride together with aluminum chloride and ferric chloride, the latter chlorides in an amount between 10 and 1000 times the equivalent of the gallium, and where the concentration of said hydrochloric acid solution is such that the total chlorine ion concentration is 5.0 N to 10.0 N, the concentration of free hydrochloric acid is less than 7.0 N, but greater than the molar amount of gallium included said trialkyl phosphate being employed in a molar amount to provide 015 to 1.5 times the moles of ferric chloride in the aqueous phase for transferring to the solvent a major portion of gallium in the aqueous phase together with a minor portion of ferric chloride, washing with water the solvent after the extraction, extracting from the solvent the gallium and the ferric chloride in the aqueous phase and reusing the solvent for the extraction of gallium and ferric chloride from a fresh supply of hydrochloric acid solution.

3. A process according to claim 1 which comprise subjecting said hydrochloric acid solution to counter-current multistage extraction by use of said trialkyl phosphate wherein the molar ratio of trialkyl phosphate to ferric chloride in the hydrochloric acid solution is 0.15 to 1.5, thereby transferring to the solvent a major portion of gallium in the aqueous phase together with a minor portion of ferric chloride.

4. A process according to claim 1 wherein said trialkyl phosphate is diluted with an inert hydrocarbon selected from the group consisting of benzene, n-hexane, ligroin, and kerosene and is employed as a solution at a trialkyl phosphate concentration of 1 to 90% by volume.

5. A process according to claim 1 wherein said trialkyl phosphate is tri-n-butyl phosphate.

6. A process according to claim 1 which comprises subjecting said hydrochloric acid solution to counter-current multistage extraction by use of said trialkyl phosphate wherein the molar ratio of trialkyl phosphate to 15 References Cited in the file of this patent UNITED STATES PATENTS 2,227,833 Hixson et a1. Jan. 7, 1941 2,743,170 Burger Apr. 24, 1956 2,767,047 Wilhelm et a1 Oct. 16, 1956 OTHER REFERENCES Liquid-Liquid Extraction Procedures in Inorganic Analysis, T. S. West, Metallurgia, April 1956, July 1956. 

1. A PROCESS FOR SEPARATING AND EXTRACTING GALLIUM FROM A MAJOR PORTION OF FERRIC CHLORIDE COEXISTING THEREWITH IN AN AQUEOUS HYDROCHLORIC ACID SOLUTION WHICH COMPRISES ADDING TRIALKYL PHOSPHATE SOLVENT HAVING 8 TO 25 CARBON ATOMS TO A HYDROCHLORIC ACID SOLUTION CONTAINING GALLIUM CHLORIDE TOGETHER WITH FERRIC CHLORIDE, THE LATTER IN AN AMOUNT BETWEEN 10 AND 1000 TIMES THE EQUIVALENT OF THE GALLIUM, AND WHERE THE CONCENTRATION OF SAID HYDROCHLORIC ACID SOLUTION IS SUCH THAT THE TOTAL CHLORINE ION CONCENTRATION IS BETWEEN 5.0 N TO 10.0 N THE AMOUNT OF FREE HYDROCHLORIC ACID THE CONCENTRATION OF FREE HYDROCHLORIC ACID IS LESS THAN 7.0 N, BUT GREATER THAN THE MOLAR AMOUNT OF GALLIUM INCLUDED AND THE MOLAR AMOUNT OF SAID TRIALKYL PHOSPHATE IS 0.15 TO 1.5 TIMES THE MOLAR AMOUNT OF FERRIC CHLORIDE IN THE AQUEOUS PHASE TOGETHER WITH A MINOR PORTION OF FERRIC CHLORIDE, WASHING WITH WATER THE SOLVENT AFTER THE EXTRACTION, WHEREBY THE GALLIUM AND FERRIC CHLORIDE ARE EXRTRACTED FROM THE SOLVENT AND THE SOLVENT MAY BE USED FOR THE EXTRACTION OF GALLIUM AND FERRIC CHLORIDE FROM A FRESH HYDROCHLORIC SOLUTION. 